1. Field of the Invention
This invention relates to a method and system for controlling and sampling of batch processes employed for the treatment of water and wastewater. More specifically, the method and apparatus of the invention provides a means of synchronizing sampling of batch water and/or batch wastewater treatment processes for adjustment and control of the batch treatment processes.
2. Description of Background Art
Over the past 10 years there has been a revival of use of the sequencing batch reactor (SBR) used for suspended growth activated sludge processes because of the inherently more efficient batch settling and often higher treatment efficiency for batch organic contaminants removal than is possible with the conventional continuous flow activated sludge process. The process employed in a SBR is often is referred to as the SBR process which uses the same vessel for batch biological reactions and quiescent batch settling. Thus, the SBR process eliminates the major cost of dedicated final clarifiers necessary for the conventional activated sludge process as well as improving solids removal performance.
However the SBR process has several disadvantages, the principal one being that it does not operate with a constant level and continuous flow, but requires intermittent operation for cycles of fill, react, settle, decant, waste and idle. Typical sequence level fluctuations are 30% to 50% of the maximum operating depth or as much as 5 to 10 feet of level fluctuations. The result is a much lower use to total volume ratio than the conventional activated sludge process. Accordingly, the SBR process is generally not cost effective for flows greater than five to ten million gallons per day (MGD).
Another disadvantage of the SBR process is that significant head loss occurs from the influent to the final effluent, requiring additional energy and pumping costs. Additionally, because the effluent flow is not continuous, flow equalization systems may be required to prevent peak loadings and adverse impacts on waters receiving the effluent from the SBR process as well as downstream processes.
Still another disadvantage of the SBR process is the requirement for labor-intensive operation under conditions of varying hydraulic and organic loadings. Since the SBR process reactors operate based on levels and timers any variation in loading requiring adjustments cannot be determined unless operating personnel are in attendance for the complete batch treatment sequence and manually sample or trigger a sampler in synchronization with the prevailing level and timer settings.
Finally, the basic process and design limitations of the SBR process make it difficult to achieve the same high efficiency biological nutrient removal possible using the continuous flow activated sludge process, especially in a small system and those subjected to wide variations in either hydraulic or organic loadings, or both.
Several improvements have been attempted to overcome the limitations of the conventional SBR process. A continuous inflow, partitioned SBR process is disclosed in U.S. Pat. No. 4,468,327, and cyclically operated intermittent flow path sequential cycle, multi-zoned recycle SBR process disclosed in U.S. Pat. Nos. 4,663,044 and 5,013,441. Significant level fluctuations, head losses and intermittent high flow rate discharges, however, still prevent these processes from overcoming all the limitations of the conventional SBR process.
Attempts have also been made over the years to overcome the level variation limitations of all SBR type processes and the cost of dedicated final clarifiers for the conventional activated sludge process. U.S. Pat. No. 3,470,092 illustrates a first attempt to develop a new suspended growth activated sludge process utilizing the concepts of both batch treatment and continuous flow. This two cell process was partially interconnected at the water surface. The alternate cell feed concept was not effective because it did not achieve a high treatment efficiency, had a low aerator utilization factor, and required long detention times to operate, resulting in expensive systems. U.S. Pat. No. 4,179,366 discloses addition of a third bottom interconnected cell, but also suffered from low treatment efficiency and ineffective changeover of untreated wastewater from the first cell to the third cell. The processes disclosed by both patents also required significant level fluctuations in the treatment cells between operating cycles which made it difficult to control flows and operate fixed, level-sensitive mechanical aeration systems.
German Patent No. 3,147,920 discloses the same three cell concept as U.S. Pat. No. 4,179,366. Although this three cell process achieved a more constant level, and overcame some of the limitations of the prior art, the process failed because it relied on expensive and unreliable mechanical gates to separate the treatment cells at various cycle times, and because treatment efficiency and effectiveness was too low to be commercially useful.
French Patent No. 2550522 describes another constant level apparatus including three separate, identical basins. This process required a large, expensive treatment system because three independent basins were required, only ⅓ of the total treatment volume was used for biological treatment at any time, and only ⅓ of the aeration equipment could be used at one time.
In spite of these attempts to improve on the performance and effectiveness of the SBR and conventional activated sludge processes, they do not provide higher treatment efficiency and hence they are not significantly more cost effective. Such attempts have either failed to totally achieve the desired benefits, or have new inherent disadvantages, which result in little or no net benefits compared to conventional methods.
Prior attempts to develop constant level processes to improve on the conventional suspended growth activated sludge process rely on the management control and recycle of mixed liquor suspended solids by back flushing or forward flushing through or around the treatment system by control of the timing and direction of wastewater flow into and through the treatment system. These methods of solids management differ significantly from variable level SBR""s, and also differ from the constant level conventional activated sludge process, which settles the mixed liquor suspended solids in a dedicated final clarifier to collect and recycle the resulting activated sludge back to the aeration basin.
Sewage treatment systems are typically batch operations, flow-through (continuous) operations or a combination thereof. Various schemes, such as back-mixing and the like, are practiced. For relatively small operations which are capital-constrained, batch treatment is usually employed. Typical waste batches contain ammonia, which can be treated, such as with certain aerobic autotropic organisms, to oxidize ammonia to nitrite and then further treat the batch to oxidize the nitrite to nitrate. This is the well-known nitrification process in sewage treatment. To complete elimination of ammonia, the nitrites and nitrates are reduced to nitrogen gas, e.g. denitrification. An aspect of batch sewage treatment, is measurement during treatment of the oxygen consuming potential. Several methods of measurement are used including measuring BOD (e.g. xe2x80x9cBiological/Biochemical Oxygen Demandxe2x80x9d). Accordingly, batch sewage treatment completion and process timing can be measured as a function of the concentration of ammonia (NH3), nitrates/nitrites (NOX), and BOD. Effective use of the measurement of these parameters is important to the economic viability of efficient batch sewage treatment operations. Such measurements are initiated by sampling of the waste being treated.
Biological nitrogen removal is a two-step process consisting of nitrification and denitrification. Nitrification occurs in the presence of oxygen by microorganisms, which oxidize ammonia to nitrate. Nitrification can occur in (1) suspended growth processes such as activated sludge, (2) in attached growth processes such as trickling filters, or (3) in combined processes such as trickling filters followed by activated sludge. A key characteristic of nitrifying organisms is that they grow more slowly than the microorganisms associated with carbonaceous BOD removal, therefore longer solids retention times are essential for nitrification to occur. Nitrification also consumes 4.6 pounds of oxygen and 7.1 pounds of alkalinity per pound of ammonia oxidized.
Nitrification is simply a nitrogen conversion process as it changes nitrogen from one form (ammonia) to another form (nitrate). While nitrogen is thus changed from a potentially toxic form with a relatively high oxygen demand to a less toxic form that does not impose an oxygen demand, total nitrogen, which is the sum of all forms of nitrogen, is not reduced. For complete biological nitrogen removal, denitrification must occur.
In biological denitrification, a different group of microorganisms uses the nitrates produced during nitrification as an oxygen source and in so doing transform nitrate to nitrogen to nitrogen gas, which then dissipates to the atmosphere. Denitrifying microorganisms require an anoxic environment free of molecular dissolved oxygen (D.O. less than 0.5 mg/L), along with a soluble, or dissolved, organic food source. Soluble BOD, methanol, acetate, or the volatile fatty acids from fermented sludge can serve as this food source. As with nitrification, denitrification can occur in either suspended growth, attached growth or combined processes. Denitrification produces 3.6 pounds of alkalinity per pound of nitrate reduced to nitrogen gas.
Conventional sampling instrumentation for batch sewage treatment operations is not designed by synchronizing sampling during the treatment process. Typically, a human operator does not perform multiple sampling of the various process steps during the course of a batch treatment of sewage. That is if there is no multiple sampling, no analysis of the sample is performed and a decision made as a result thereof to adjust the sampling regime during the actual sewage treatment operation. Rather, the operating step of the process are preset into the equipment by the manufacturer. The actual batch processing parameters commonly remain unchanged during the sewage treatment operation, regardless of changes in conditions or errors in the assumption that these parameter settings will address changes in conditions. For instance, in a given process the treatment of the sewage might progress faster than originally called for by the equipment manufacture, or the nature and/or the quantity of materials in the treatment tank might change. These changes, if known via sampling procedures, would have made a difference in the operating regime decided upon. As can be appreciated by those in the art, the operator of batch sewage treatment equipment is typically not the same person that performs an analysis of the samples obtained from the equipment. In real life terms, the sample must be processed and analyzed and the resulting data therefrom compared to known operating parameters, so that an operator can decide whether or not a particular stage of the treatment process has been completed. Present methods of operating a batch sewage treatment systems can result in inconsistent performance, without benefit of ongoing process adjustments for the sewage being treated. Thus, there is needed a method of operating a batch sewage treatment process which permits synchronous sampling. An operator can perform analysis of the samples to determine how the overall sewage treatment process is performing.
This present invention is a method and apparatus, or system, for the determination of the performance of each step or phase or all of the steps or phases of an SBR biological treatment process via synchronous sampling for analysis. The results of such sampling and analysis are employed to effect changes in the timers and controls of the SBR process. The method of the invention provides sychronized sampling to achieve more reliable treatment of the water and wastewater by, inter alia, reducing the amount of manual labor required for sampling of the wastewater treatment process.
According to one aspect, the present invention provides for synchronized sampling during operation of a sequencing batch reactor (SBR) process to enable an operator to sample one, several or all phases of the SBR Process and by analysis of the samples taken determine the effectiveness of the sampled phase or process.
In another aspect the present invention eliminates the disadvantages of prior art attempts to improve on SBR and conventional activated sludge processes by employing PLC controllers for process control without benefit of process analysis and performance feed back via synchronized sampling and/or analysis.
In yet another aspect the present invention provides a method for automatically sampling the treatment processes.
In still another aspect the invention provides a low cost method for synchronized sampling of the wastewater treatment processes.
In a still further aspect, the present invention provides the ability to obtain samples capable of being employed for the determination of the performance of the treatment processes in synchronization with the controls and timers provided by the manufacturers of the treatment plant equipment.
In yet a further aspect the present invention permits a user to modify and optimize existing control systems for water and wastewater treatment as a result of synchronized sampling and analysis of the samples from the treatment processes.
Another aspect the present invention makes it possible to more efficiently operate an SBR or other batch water and/or wastewater treatment process under varying organic loading and hydraulic loading conditions.
The present invention provides an improvement to the prior art and allows, automated control of the operation of sampling equipment by extracting or retrieving samples generated by sampling equipment, to permit analysis of such samples. The results of the analysis when compared to known operating parameter(s) permits modification in the sampling regime of the equipment and/or the overall process settings for the SBR.